(A) Field of the Invention
The present invention refers to a gear shift device for bicycles, of the type comprising:
at least one derailleur, having a first body destined to be attached to a bicycle frame and a second body that can be displaced with respect to the first body to cause the selective engagement of a bicycle chain on a number of sprockets, to achieve the various gears of the device,
an electric actuator to drive the displacement of the second body of the derailleur,
electronic control means for controlling said electric actuator,
manually-operated activating means, connected to said electronic control means, to cause activation of said electric actuator in order to select the required gear,
means for detecting the position of said second body of the derailleur and for indicating said position to said control means, so as to permit the automatic disabling of the electric actuator once the required position has been reached,
in which said electric actuator is directly associated with said derailleur.
A gear shift device of the kind outlined above is described and illustrated in U.S. Pat. No. 5,480,356, a patent held by the same applicant.
(B) Description of the Related Art
FIG. 1 of the attached drawings illustrates a racing bicycle, indicated as a whole by reference number 1, comprising a frame 2 constructed, in a well-known manner, of tubular elements comprising stays 3 for supporting the rear wheel 4. Reference number 5 indicates a fork for supporting a front wheel 6, associated with a handlebar 70, which is also made with a tubular structure.
In its lower part, the frame 2 carries a crankset 7 of substantially conventional type for driving the rear wheel 4 by means of a gear shift device made according to the present invention, indicated globally by the number 8.
The gear shift device 8 essentially includes a rear assembly 9 and a front assembly 10 comprised, in a well-known manner, of a number of sprockets 11 of various diameters, co-axial with the axle A of the rear wheel 4, and a number of crown wheels 12, also of various diameters, co-axial with the axle B of the bicycle""s crankset 7.
The sprockets 11 and the crown wheels 12 can be engaged selectively by a chain transmission forming a closed ring 13 to achieve the different gear ratios available by means of the gear shift device 8, by activating a rear derailleur 14 forming part of the rear assembly 9 and a front derailleur 15 belonging to the front assembly 10.
FIG. 2 in the enclosed drawings illustrates the rear derailleur 14 made according to the solution proposed in U.S. Pat. No. 5,480,356. The rear derailleur 14 includes a first body 16 that is designed to be attached to the bicycle frame and a second body 17 connected to the first body 16 by means of a parallelogram linkage comprising two arms 18 and 19, the ends of which are articulated at 20, 21 and 22, 23 to the two bodies 16 and 17. The second body 17 includes, in a well-known manner, a rocker arm 24 that carries-the chain transmission wheels 25 and 26.
Reference number 27 indicates an electric actuator, in the form of an electric motor combined with a reduction gear, that is directly incorporated in the derailleur 14 to drive the displacement of the second body 17, and consequently also of the rocker arm 24, through the various engagement positions of the chain 3 with the sprockets 11.
FIG. 3 in the enclosed drawings illustrates the motor and reduction gear assembly 27 forming the object of the device described in U.S. Pat. No. 5,480,356. In said Figure, the body of the motor and reduction gear assembly 27, indicated as 28, is shown on a larger scale and in cross-section. The body 28 contains not only the motor 35, but also an epicycloid reduction gear 29 connected to the shaft coming from the electric motor 35. The epicycloid reduction gear 29 drives the rotation of a screw 30. As shown in FIG. 2, the body 28 of the motor and reduction gear assembly is attached with an articulated coupling to the body 16 of the derailleur around an axis 22, while the screw 30 engages a nut screw 31, the body of which is mounted in an articulated manner around an axis 21 on the body 17 of the derailleur. As a result, the motor and gear reduction assembly lies along a diagonal of the parallelogram linkage and the turning of the motor causes a corresponding rotation of the screw 30 by the epicycloid gearing 29, so that the nut screw 31 moves along the screw, leading to an elongation or shortening of the distance between the axes 21 and 22 of the parallelogram linkage.
As illustrated in FIG. 3, the body 28 of the motor and reduction gear assembly also contains a device 32 comprising an encoder, including an optical or magnetic sensor that co-operates in a well-known manner with a disc 34 carried by the screw 30.
The electric power to the motor and reduction gear assembly 27 is provided by means of a battery 37 (FIG. 1) conveniently housed in one of the tubes of the bicycle frame 2 or, alternatively, in one side of the handlebar 70, or inside the container of a microprocessor control unit 40 (only partially visible in FIG. 1) that may be attached, for instance, to the bicycle frame in the area of the crankset and is used to control the electric motor 35 on the basis of signals originating from two manually-operated control levers 43 and 44 (which could also be replaced by two buttons) associated, in a well-known manner, with a brake lever 41 (FIG. 1). The microprocessor unit 40 is also connected to the encoder 32, which detects the angular position of the screw 30, and consequently of the rear derailleur, so as to stop the electric motor when a required transmission gear has been reached, said gear being selected by manually operating the levers 43 and 44 (which are operated to shift the chain into higher or lower gears, respectively). The connections between the aforementioned electric components are made, in the case of the above-mentioned well-known solution, by means of wires (not shown in the drawings) conveniently positioned inside the tubes of the bicycle frame 2.
The above-mentioned earlier document describes the opportunity to use an encoder of any kind to provide the means for detecting the position of the second body of the derailleur. In the course of experience gained in the past by the applicant, an incremental encoder was used. With this type of transducer, however, any interruption in the electric power supply to the encoder made it necessary to provide for a procedure for re-calibrating the encoder by making the derailleur move to the position taken as the zero reference by the encoder. It is also important to bear in mind that there is an increasingly-felt need to increase the autonomy of the bicycle with battery-powered systems and therefore to reduce the consumption of electrical energy. For this purpose, control systems can be used that enable energy to be delivered only for the amount of time it takes to satisfy the requirement, after which the system returns to a low-consumption regime.
It is also true that, even using an incremental transducer, strategies can be adopted to keep the position value detected memorized at logic level in the control unit. However, this solution may not be sufficient to guarantee the reliability of the transducer, because while it is not being powered the position of the second body of the derailleur may undergo small variations due to the vibrations to which the bicycle is liable while in motion.
The purpose of the present invention is to achieve a gear shift device of the type outlined at the beginning of this description, in which the means for detecting the position of the movable body of the gear always guarantee a reliable and accurate indication of said position, even in the event of an interruption in the power supply, for instance.
With a view to achieving said purpose, the object of the invention is a gear shift device having all the characteristics illustrated at the beginning of this description and characterized, moreover, in that the detection means are comprised of an absolute electric transducer associated with said derailleur and designed to produce an electric signal indicating the absolute position of said second body of the derailleur.
Thanks to said characteristic, the transducer is always capable of providing accurate information on the position of the second body of the derailleur, without requiring any re-calibration procedures after an interruption in the power supply.
In a preferred embodiment, said transducer is a potentiometer comprising at least one electrically-conducting track and a contact sliding on said track due to the effect of any movement of said second body of the derailleur with respect to the first body. In a first example of said embodiment, said potentiometer is of the rotating type, comprising at least one circular track and one rotating movable contact engaged on said track. In a second example, the potentiometer is a sliding potentiometer comprising a cylinder carrying the aforementioned track and a rod carrying the movable contact that slides inside the cylinder.
The absolute transducer can be associated directly with the actuator, or it can be placed between two parts of the derailleur that move in relation to each other as a result of the movement of said second body with respect to the first body. For instance, in the case in which the derailleur has a parallelogram linkage that connects the first body to the second body, a rotating potentiometer can be used in association with any of the articulations of the parallelogram linkage, or a sliding potentiometer can be arranged between two parts of the parallelogram linkage that move in relation to each other, or between the body of the motor and a nut screw that engages a screw driven by the motor.
In the case of the potentiometer being mounted on the shaft of the actuator, it is preferable for it to be placed downstream from a reduction device so that the potentiometer performs less than one turn when the derailleur moves between its two end positions. Otherwise, a reduction gear can be provided in the potentiometer itself or, alternatively, means for counting the turns of the shaft on which the potentiometer is installed can be provided together with the potentiometer.
The absolute transducer may not necessarily be a potentiometer; for instance, it could be a transducer of optical or magnetic type, such as a Hall-effect transducer.